The invention generally relates to the overall construction and configuration of a proton exchange membrane fuel cell, and more particularly, the invention relates to a combined fuel cell flow plate and gas diffusion layer.
A fuel cell is an electrochemical device that converts chemical energy produced by a reaction directly into electrical energy. For example, one type of fuel cell includes a proton exchange membrane (PEM), a membrane that may permit only protons to pass between an anode and a cathode of the fuel cell. At the anode, diatomic hydrogen (a fuel) is oxidized to produce hydrogen protons that pass through the PEM. The electrons produced by this oxidation travel through circuitry that is external to the fuel cell to form an electrical current. At the cathode, oxygen is reduced and reacts with the hydrogen protons to form water. The anodic and cathodic reactions may be described by the following equations: EQU H.sub.2.fwdarw.2H.sup.+ +2e.sup.- at the anode of the cell, and EQU O.sub.2 +4H.sup.+ +4e.sup.-.fwdarw.2H.sub.2 O at the cathode of the cell.
Because a single fuel cell typically produces a relatively small voltage (around 1 volt, for example), several serially connected fuel cells may be formed out of an arrangement called a fuel cell stack to produce a higher voltage. The fuel cell stack may include different plates that are stacked one on top of the other in the appropriate order, and each plate may be associated with more than one fuel cell of the stack. The plates may be made from a graphite composite material or metal and may include various channels and orifices to, as examples, route the above-described reactants and products through the fuel cell stack. Several PEMs (each one being associated with a particular fuel cell) may be dispersed throughout the stack between the anodes and cathodes of the different fuel cells. In addition to the membrane, a catalyst and gas diffusion layer are sandwiched between the anode and cathode plates. The catalyst layer may be placed on the membrane or on the gas diffusion layer. The gas diffusion layer may be made out of an electrically conductive and porous diffusion material, such as a carbon cloth or paper material, for example.
Referring to FIG. 1, as an example, a fuel cell stack 10 may be formed out of repeating units called plate modules 12. In this manner, each plate module 12 includes a set of plates that may form several fuel cells. For example, for the arrangement depicted in FIG. 1, an exemplary plate module 12a may be formed from a cathode cooler plate 14, a bipolar plate 16, a cathode cooler plate 18, an anode cooler plate 20, a bipolar plate 22 and an anode cooler plate 24 that are stacked from bottom to top in the listed order. The cooler plate functions as a heat exchanger by communicating a coolant through coolant flow channels that are formed in either the upper or lower surface of the cooler plate to remove heat from the plate module 12a. The surface of the cooler plate that is not used to route the coolant includes flow channels to route either hydrogen (for the anode cooler plates 18 and 24) or oxygen (for the cathode cooler plates 14 and 20) to an associated fuel cell. The bipolar plates 16 and 22 include flow channels on one surface to route hydrogen to an associated fuel cell and flow channels on the opposing surface to route oxygen to another associated fuel cell. Due to this arrangement, each fuel cell may be formed in part from one bipolar plate and one cooler plate, as an example.
For example, one fuel cell of the plate module 12a may include an anode-membrane-ecathode sandwich, called a membrane-electrode-assembly (MEA), that is located between the anode cooler plate 24 and the bipolar plate 22. In this manner, the upper surface of the bipolar plate 22 includes flow channels to route oxygen near the cathode of the MEA, and the lower surface of the anode cooler plate 24 includes flow channels to route hydrogen near the anode of the MEA.
As another example, another fuel cell of the plate module 12a may be formed from another MEA that is located between the bipolar plate 22 and the cathode cooler plate 20. The lower surface of the bipolar plate 22 includes flow channels to route hydrogen near the anode of the MEA, and the upper surface of the cathode cooler plate 24 includes flow channels to route oxygen near the cathode of the MEA. The other fuel cells of the plate module 12a may be formed in a similar manner.
In order to manufacture the fuel cell stack in a cost effective manner, the time that is required to assemble the stack needs to be minimized. One way to accomplish this is to minimize the number of components that are handled in the assembly of the stack.